It's hard to say, because running slowly can also be caused by your HD (its type and speed or how full it is) or other things. Are you sure that RAM is the cause of the problem? If you share the model or stats of your computer, we might be able to make a better recommendation. I'd hate to see you splurge on the 8 GB of RAM and then find out it doesn't solve your problem!
Here are my laptop specs
Product name HP Notebook - 15-ay148tx
Microprocessor Intel® Core™ i5-7200U (2.5 GHz, up to 3.1 GHz, 3 MB cache, 2 cores)
Memory, standard 8 GB DDR4-2133 SDRAM (1 x 8 GB)
Video graphics AMD Radeon™ R5 M430 Graphics (2 GB DDR3 dedicated)
Hard drive 1 TB 5400 rpm SATA
Currently my hard drive has less than 150GB full so I'm pretty confident that hard drive space is not an issue here
To give a bit more background this is what was happening - I've had no problems prior to this layout and none after. My laptop is only 7 months old so its not old by any stretch
I've been working on a layout for awhile and suddenly weird things are happening when I am duplicating and moving items around, bringing papers in, copying layer styles just to name a few. When I am duplicating items and moving them around or copying layer styles they arent duplicating or copying correctly and I am left with "stamps of colored areas" on both the original item and the new one, when I bring papers in they are being cut into strips as they are coming over to the template when they are fine in their original file. The problem areas on the layout are the white patches (not the white strokes I've added to my photos)